Limited Utility of Lymphocyte-Based Inflammatory Indices in Troponin-Negative Unstable Angina Pectoris

Background: This study investigated the role of lymphocyte-based inflammatory indices (LBIIs) in predicting severe coronary artery disease (CAD) in patients undergoing coronary angiography (CAG) for unstable angina pectoris (USAP). Methods: Records of patients who underwent CAG between January 2023 and December 2024 were retrospectively reviewed. The patients were divided into two groups based on coronary artery stenosis severity: non-severe CAD (<70% stenosis) and severe CAD (≥70% stenosis). Demographic data, risk factors, and complete blood count parameters were recorded. Six LBIIs were calculated: the neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), Systemic Immune–Inflammation Index (SII), Systemic Inflammatory Response Index (SIRI), and Systemic Immune–Inflammatory Response Index (SIIRI). Diagnostic performance was evaluated using logistic regression and ROC curve analyses. Results: Out of 505 patients, 234 (46.3%) had severe CAD. Among the six LBIIs, only the SII differed significantly between groups in univariate analysis and showed moderate discrimination in the ROC analysis (AUC 0.71; 95% CI 0.661–0.762; p < 0.001; sensitivity 76.2%; specificity 56.1%). However, the SII was not an independent predictor in the multivariate analysis. Conclusions: LBIIs (NLR, MLR, PLR, SII, SIRI, and SIIRI) do not provide a clinically significant and independent contribution to predicting severe CAD in USAP patients undergoing CAG. Although the SII performed moderately well in the univariate analysis, it lost independence in the multivariate analysis and is thus not suitable for use as a standalone marker in clinical decision-making.